Recently, there have been various reports on the benefit which tryptophan is believed to have on several aspects of human behaviour, mood, brain function, brain development, when such tryptophan is taken up by the brain. Examples of such reports are WO 99/55174, WO 00/42868, WO 2005/023017.
Tryptophan is an amino acid present in many proteins, like e.g. whey proteins, but also animal protein contains tryptophan. Tryptophan can be taken up in the blood, and from the blood into the brain, after ingestion of a protein which contains tryptophan. However, tryptophan is not the only amino acid taken up, and in fact when an average animal protein composition is ingested, the level of tryptophan taken up by the brain is so low due to competitive uptake of other amino acids that usually no significant effect can be observed attributable to tryptophan. Hence, most of the reports referred to above either use proteins or protein-fractions rich in tryptophan, or the free amino acid tryptophan (the latter optionally in combination with other free amino acids and/or proteins).
Use of tryptophan as free amino acids has disadvantages, in that food legislation in many countries limits the use of tryptophan as free amino acid in foodstuffs.
Tryptophan-rich proteins have natural limits to the level of tryptophan and its ratio to large neutral amino acids, which is relevant for uptake of tryptophan by the brain.
Recent insight is that peptides rich in tryptophan can be a good source to get sufficient tryptophan in the brain for the desired effects and may be easier applied in foodstuffs than free amino acids. Such peptides rich in tryptophan are preferably low in amino acids with which competition in uptake into the brain is believed to be high: the so-called large neutral amino acids (LNAA), which are: leucine, isoleucine, valine, tyrosine, phenylalanine (and depending on the definition of LNAA one uses also methionine). Hence, it is preferred to provide peptide preparations which contain a high level of tryptophan and have a high ratio tryptophan/LNAA. Methionine is considered not to have any beneficial metabolic effect in the context of this invention, and is thus for the purpose of this invention not considered as one of the LNAA.
EP 661004 discloses animal feed comprising tryptophan in combination with e.g. dextrin. Said composition is for maintaining growth and increase of body weight at high environmental temperatures when the animals have low appetite.
WO 2004/112803 discloses methods for managing the symptoms of premenstrual syndrome by providing a composition containing a protein having a high tryptophan/LNAA ratio, in combination with rapidly digestible carbohydrates.
WO 2006/130567 discloses methods for treating winter blues, seasonal affective disorder (SAD), and depressive disorders; and carbohydrate craving, weight gain, and mood symptoms associated with same, by administering to a subject a carbohydrate-rich composition with minimal protein content, or a carbohydrate-rich composition that contains tryptophan or a tryptophan-rich protein or peptide.
In US2003039739 compositions and methods of losing weight are described that are suitable for individuals susceptible to gastric hyperacidity or gastroesophageal reflux. The compositions include in part a snack food having two or more rapidly digestible carbohydrates, in which the foodstuff or an aqueous mixture of the foodstuff and water has a pH equal to or greater than about 6, and in which the snack is substantially protein-free. The experimental/test plan of the invention allocated the amounts of protein and carbohydrate differently at each meal and snack to ensure that following the lunch and dinner meals, the ratio of plasma tryptophan to that of the circulating large neutral amino acids is not decreased so that the ratio would be significantly elevated following the consumption of the carbohydrate-rich snack.
In WO02/46210 a method for increasing the level of tryptophan in whey protein hydrolysates is described. In the method used, whey is first hydrolysed at acidic pH by one or more acid proteases, preferably by a pepsin, rennin, acid fungal protease, chymosin, papain, bromelain, chymopapain or ficin. The preferred incubation conditions are between pH 1.5 and 3.5 and were chosen to generate peptides having a hydrophobic nature. The hydrolysis is deliberately carried out in such a way that the tryptophan residues become incorporated in large, hydrophobic peptides. Due to the fact that tryptophan is present in relatively large peptides, the tryptophan uptake into the blood will be retarded hereby limiting the application possibilities of the preparation as a food or beverage ingredient, especially in combination with other proteins. Another disadvantage of the use of such large peptides is that such peptides may give rise to allergic reactions. Such reactions to whey proteins are well known.
WO 2008/052995 relates to tryptophan-containing peptides, which further may contain carbohydrates.
Insulin may selectively promote uptake of the LNAA by various tissues, thus making more tryptophan available for uptake in the brain, as the LNAA compete with tryptophan for uptake in the brain. Thus, considerable levels of plasma insulin may be beneficial for the desired effects of tryptophan on the brain. Such desirable effects are related to the field of brain function, alertness, sleep, mood, concentration, and related issues. High plasma insulin levels may be promoted by presence of fast digestible carbohydrates together with a tryptophan containing composition, but such may lead to either a dip in blood glucose e.g. about 2 hours after ingestion and/or not being able to maintain considerable levels of blood glucose for e.g. 3-4 hours for the brain to have maximum benefit of the tryptophan and/or for optimal brain function, alertness, sleep, mood, concentration, cognition in general and related fields.